Upgrade can mean so many things. I put a set of wheels with Chukker rims, 36 spoke 3 cross on Deore hubs on my 7.3 FX because I need the ability to reliably hold a heavy rider (me) while being bullet-proof for gravel riding. These wheels would be a downgrade for many other riders because of the weight of the wheels.

Light rims with lower spoke counts would be a downgrade for me, but an upgrade for many others.

As far as price, I will quote the tow truck driver from National Lampoon's Vacation when Clark Griswold asked how much it was to replace the tires on the Family Truckster... "How much do you got?" You can spend a little, or you can spend a lot... the "right" answer depends significantly on your objectives in upgrading, your budget and a cost benefit analysis based on what type of riding you do, and what you hope to improve.